This invention relates to the field of solar energy collection, and in particular to solar energy transfer structure design and construction. In recent years there has been an increase in the development and use of active solar energy collection and distribution systems. Active systems use radiant energy collecting solar cells to convert the incident electomagnetic energy into usable electric, steam or other power sources.
Solar collection units fall into two primary classifications, active solar units and passive solar units. To date the primary emphasis has been on the development of active solar collection units. In general, active solar collection units have a large number of solar collecting elements contained thereon. Such systems include those which make use of large reflectors to direct the radiant energy to a central absorber, those which have a plurality of direct solar absorbers and those providing direct solar energy conversion. In this application, the term "collector" will be used to describe all of these various types of solar collecting elements.
When using any of these systems, it is necessary to properly orient the collectors. For example, when utilizing reflectors, it is necessary to direct the energy to a central absorber. With the reflecting systems, each of the individual reflecting elements must be oriented so that, when in operation, the incident sunlight will be accurately directed and focussed onto the absorber. Additionally, as the sun's position relative to the reflectors changes, constant adjustment of the orientation of the collectors is necessary. Accurate orientation is therefore quite essential to the proper operation of the system.
With solar collecting systems, including the reflective systems, it has become standard in the industry to rotate the solar energy transfer structure in order to maintain proper orientation. In general, this has been accomplished by means of mounting the collecting elements on tracking structures which gimbal to allow the elements to remain properly oriented.
The basic design of these solar energy tracking structures are well developed and well known in the art. In general the tracking structures have been comprised of a base or mounting pedestal upon which the remaining components are mounted, a drive mechanism, a plate or mounting surface upon which the individual reflecting elements are mounted and the individual collecting elements themselves.
In the majority of the systems currently in use, these tracking structures are tied to a sensing and control system, which provide a control signal for driving the tracking structure. The tracking structures then adjust the position of the collecting surfaces so as to keep the energy properly oriented relative to the sun.
While this basic design is well known in the art, considerable effort has continued in the development of improved designs. The primary concern in the design and operation of solar energy conversion systems is the overall collection efficiency. While significant effort is continuing to be directed into the design of more efficient solar collecting elements themselves, other areas of development are also receiving considerable attention. Also, since significant numbers of these tracking structures are needed for each solar energy collection facility, the reduction in the cost of fabrication and maintenance of the structures is quite important.
One means of increasing efficiency is to increase the density of solar collecting elements that are carried on a single solar energy transfer structure. The more individual solar collecting elements a single solar energy tracking structure can carry, the more densely can solar tracking elements be placed in a given collection farm. Also, the more densely the units can be placed on the ground, the more economically the system can be built and operated. It is in this area that significant gains in system efficiency can be made.
However, in designing the larger structures, the increased size presents several other problems which must be compensated for. The first problem is that the larger and heavier the structure, the larger and more powerful must be the drive motors which are installed. This creates significant problems in terms of control and cost. The larger the solar energy transfer structure, the larger the motor required to control the structure. Also, the larger the motor required, the more difficult it is for that motor to achieve fine motion and position control.
Finally, the larger the motor having the capability of fine control, the greater will be the cost. This cost can be quite significant when multiplied by the relatively large number of solar energy transfer structures necessary for large energy farms. Added to this cost is the necessity of larger drive motors, larger drive mechanisms and gearing.
The prior art has attempted to address this problem by reducing the weight and inertia of the system by using stronger and lighter materials. This approach has met with some success.
However, this does not address the second major problem in that regardless of how much effort is put into the improvement of the materials used, the basic moving surface of the solar energy transfer structure is planar shaped, and when placed in the outdoor environment, acts as an airfoil when the natural wind blows across it. That is, when in a substantially horizontal position, the wind blowing across the planar surface places lifting loads on the structure. Then, when it becomes necessary to adjust or otherwise maneuver the structure, a greater torque loading factor must be overcome before the unit can be moved by the drive mechanism.
Some attempts have been made to alter the shape of the planar surface itself. However, this approach has met with only limited success because the critical nature of the orientation needed for the solar collecting elements. As a result, the major problem of wind forces placing undue torque loads on the planar surfaces has continued to present a major problem in the development of larger and more efficient solar energy tracking units.
What is needed therefore is a means for reducing the torque load presented to solar energy transfer structure when the solar energy transfer structure is in either an operating or a stowed mode.
It is an object of the disclosed invention to provide a means reducing the torque loading placed upon solar energy transfer structure due to lifting forces placed upon the unit by interaction of the planar surface of the solar energy transfer structure with the wind.
It is another object of the disclosed invention to provide a means for reducing the size and power of the drive mechanism needed to power a solar energy transfer structure due to the lifting forces placed upon the unit by interaction of the planar surface of the solar energy transfer structure with the wind.
It is yet another object of the disclosed invention to provide a means for increasing the efficiency of solar energy collection systems by providing a means for increasing the density at which such systems can be placed upon the ground.